1. Field of the Invention
The present invention relates to an improvement in a method for preparing a superconducting thin film of compound oxide by laser evaporation technique.
2. Description of the Related Art
Superconductivity has been thought, for a long time, to be a phenomenon observable at ultra-low temperatures realized with liquid helium as a cryogen. However, the possibility of an existence of a new type of superconducting material was revealed by Bednorz and Muller, who discovered (La, Sr).sub.2 CuO.sub.4 which exhibits superconductivity at 30.degree. K. in 1986. C. W. Chu et al. discovered, in the United States of America, another superconducting material of YBa.sub.2 Cu.sub.3 O.sub.7-.delta. having the critical temperature of about 90.degree. K. in 1987. Maeda et al discovered so-called bismuth type superconducting material. And hence, the possibility of an actual utilization of high-Tc superconductors has burst onto the scene because the superconductivity can be realized with cheap cryogen of liquid nitrogen.
The above-mentioned new type superconducting materials were obtained in a form of sintered mass prepared by powder metallurgy. But now, they can be prepared in a thin film form of very high quality.
Laser evaporation technique is one of the most promising techniques because superconducting thin films which exhibit improved superconducting properties can be prepared by the laser evaporation technique with no after-treatment such as annealing of thin films deposited on a substrate.
In the laser evaporation method, fine particles of oxide are observed on a surface of thin film obtained, although the thin film itself exhibits improved superconducting property.
Therefore, an object of the present invention is to provide a novel process for preparing a superconducting thin film of oxide possessing an improved surface property by the laser evaporation technique.